Does OS affect PC gaming performance?

My computer is currently running Windows XP and was wondering if it hinders or limits NBA 2k11's overall performance.

XP should be fine, I found I got more FPS when I upgraded from Vista to Windows 7 but you should be ok with XP

NBA 2k11 is a DX9 game so you wont be losing any feature found in DX10/11 capable OS like Vista and Win7. The only issue I see is driver support for the latest graphics cards (tbh I dont know if its a real issue or not as I havent been following driver updates outside Win7)

fps wise, my assumption is (looking at charts) the fps difference isnt by much (~5fps difference maybe, usually in favor of XP) which shouldn't matter much unless you are into benchmarking

I use Vista, never had any slowness problems except using Fraps.

I think OS does not affect your gaming experiences when playing the game, as long as you have a good maybe the best specs in your computer it will run smooth as hell.. Don't just MEET the System Requirements of the game, you must OVER MEET it. lol